Energized pre-fracturing has emerged as an effective approach for enhancing reservoir energy, fracture complexity and oil recovery in tight reservoirs. However, the mechanisms by which fracture propagation induced by different energized pre-pad fluids governs subsequent imbibition-driven oil recovery remain insufficiently understood. To address this issue, an integrated experimental framework was established to investigate the coupled evolution of fracture networks and pore-scale oil displacement during energized pre-fracturing. By combining X-ray computed tomography for quantitative fracture characterization and dynamic nuclear magnetic resonance for monitoring imbibition-driven oil recovery, the interactions between fracture-scale architecture and pore-scale fluid redistribution were systematically elucidated. The results demonstrate that, compared to conventional fracturing, energized pre-fracturing not only lowers breakdown pressure but also promotes the formation of more complex, highly connected fracture networks, which in turn substantially enhance ultimate oil recovery. Notably, gaseous pre-pad fluids exhibit clear advantages over aqueous systems, with supercritical CO₂ generating the lowest breakdown pressure and the most intricate multi-branch fracture networks, as indicated by higher fracture fractal dimension and area ratio. These fracture characteristics significantly facilitate imbibition efficiency, resulting in higher oil recovery. Pore-scale analysis further reveals that oil mobilization is dominated by contributions from micropores and mesopores, underscoring the critical role of energized pre-fracturing in activating oil stored in small-scale pore systems. The proposed multi-scale methodology, integrating fluid properties, fracture network evolution, and imbibition dynamics, provides a mechanistic basis and practical guidance for optimizing energized fracturing and improving the efficient development of tight conglomerate reservoirs.

Pulsating hydraulic fracturing (PHF) is a promising fracturing method and can generate a dynamic periodic pressure. The periodic pressure can induce fatigue failure of rocks and decrease initiation pressure of fracture. If the frequency of periodic pressure exceeds 10 Hz, the distribution of pressure along the main fracture will be heterogeneous, which is much different from the one induced by the common fracturing method. In this study, the impact of this special spatial feature of pressure on hydraulic fracture is mainly investigated. A coupled numerical simulation model is first proposed and verified through experimental and theoretical solutions. The mechanism of secondary fracture initiation around the main fracture is then discovered. In addition, sensitivity studies are conducted to find out the application potential of this new method. The results show that (1) this coupled numerical simulation model is accurate. Through comparison with experimental and theoretical data, the average error of this coupled model is less than 1.01%. (2) Even if a reservoir has no natural fracture, this heterogeneous distribution pressure can also cause many secondary fractures around the main fracture. (3) The mechanism of secondary fracture initiation is that this heterogeneous distribution pressure causes tensile stress at many locations along the main fracture. (4) Through adjusting the stimulation parameters, the stimulation efficiency can be improved. The average and amplitude of pressure can increase possibility of secondary fracture initiation. The frequency of this periodic pressure can increase number of secondary fractures. Even 6 secondary fractures along a 100 m-length main fracture can be generated. (5) The influence magnitudes of stimulation parameters are larger than ones of geomechanical properties, therefore, this new fracturing method has a wide application potential.